1. Field of the Invention
The present disclosure relates to devices, for regulating flow of a fluid through a passage, either by closing the passage or restricting it by a definite predetermined motion of the flow-element, and more particularly to a plug valve wherein the valve stem and/or actuator is associated with means to pack or seal it to prevent leakage of fluid between the inside and outside of the valve body.
2. Description of Related Art
Plug valves are mechanical devices that are frequently utilized to regulate the flow of fluids such as liquids, gases and slurries over a wide range of temperatures and pressures. These valves are used in a variety of applications, particularly industrial applications (e.g. refining, chemical, petrochemical, pharmaceutical, etc.) Plug valves may be operated manually by hand or operated mechanically with pneumatic, hydraulic, or electric actuators.
Most valves, including plug valves, are generally provided with a passage containing a flow-element that is positioned within the passage. The flow-element regulates the fluid flow through the passage either by closing the passage or restricting it by a definite predetermined motion of the flow-element. The flow-element has an open position, which allows the fluid to flow through the passage, and a closed position that prevents the fluid from flowing through the passage. The flow-element is typically connected to a stem, which actuates the flow-element, either manually or mechanically, between the open position and closed position. The flow-element for a plug valve is typically a cylindrical or conically-tapered plug, which may be rotated inside the valve body to control flow through the valve. The flow-element has one or more hollow passageways extending through it. When the flow-element is in the open position, the passageway is substantially aligned with the passage thereby enabling a fluid to pass through the passage when it is in the open position.
Plug valves may also be provided with a bonnet, which is fastened to the body of the valve to secure the flow element and stem/plug in place as well as any sealing or packing. However, over time a valve stem/plug may be frequently moved between the open position and closed position, which may expose the bonnet to rotational stress thereby loosening the bonnet. This can cause the fluid to leak from the valve, which is very undesirable because it can undermine the ability of the valve to control and isolate flow, which can lead to increased maintenance time and costly process downtime. Moreover, in recent years, environmental regulations have placed a greater emphasis on reducing leaks and other fugitive emissions from valves in industrial settings by imposing fines and other penalties on facilities that exceed allowable levels making any fluid leakage undesirable.
In light of the foregoing, various solutions have been proposed to prevent plug valve stem and bonnet leakage between the inside and outside of the valve. One such solution is a conventional sealing system that utilizes a stem seal secured into position around the valve stem using fasteners such as bolts. Although this system can prevent leakage around the plug valve, it also presents problems of its own. In particular, as a result of exposure to demanding environmental and operating conditions, the integrity of the seal can become reduced over time and make the seals prone to leakage.
For example, valves may be exposed to wide and rapid temperature changes, i.e. thermal cycling, causing its seals to contract and expand rapidly, which may degrade the seal over time and impact the reliability of the valve. In addition, the reliability of a valve seal may be impacted by vibrations and rotational forces. For example, during operations, a stem seal is often exposed to rotational forces as a valve is moved between its open and closed position, which can degrade the integrity of the seal. Additionally, valves are often exposed to high pressure operating conditions and pressure drops, which cause vibrations that may degrade the seal,
Once the seal begins to degrade, fluid often begins to leak from the inside to the outside of the valve. The valve must typically be removed from service for repair in order to prevent further leakage, which leads to costly process downtime and maintenance. One available option to prevent further leakage is to further tighten the adjustment bolts to secure the plug seal into place. However, this option requires intervention from operations personnel. Moreover, the additional force required to tighten the bonnet bolts can damage the valve, its components and significantly increase the valve operating torque.
Accordingly, in light of the foregoing, a need exists for an improved and more robust plug valve and stem sealing assembly capable of preventing leakage under demanding environmental and operating conditions while also improving the reliability of the valve seal and reducing maintenance needs.